Method for the preparation of stable and pure glyoxylic acid



United States Patent 4 Claims. (a. 260-530) It is known that it is possible to manufacture aqueous solutions of glyoxylic acid by oxidation of the glyoxal by means of nitric acid, this oxidation being followed, if so required, by concentration under vacuum. The technical solutions of glyoxylic acid obtained are, however, impure by virtue of the presence, apart from the unconverted glyoxal, of relatively large proportions of oxalic acid and nitric acid which are furthermore responsible for the instability of the solutions.

In fact, during the course of the process of oxidation of the gyloxal to glyoxylic acid, oxalic acid is formed as a secondary product; furthermore, there always remains in these solutions nitric acid and/or decomposition products of nitric acid, that is to say oxidizing nitrogenized products.

Now, nitric acid and its oxidizing derivatives continue to produce in the glyoxylic acid solutions an oxidation to oxalic acid.

In addition, when the solution resulting from the oxidation is subjected to concentration, the quantity of glyoxylic acid which was present after the oxidation operation is considerably reduced as a result of oxidation to oxalic acid, to the detriment of the glyoxylic acid. In other words, the yield of glyoxylic acid recorded after the oxidation operation falls to a very much lower value after the preparatory operations. In addition, the glyoxylic acid solutions obtained, even after concentration, still comprise oxidizing nitrogenized products, which render them unstable during storage. These technical solutions also contain oxalic acid and unconverted glyoxal.

In order to achieve an optimum efficiency of oxidation to glyoxylic acid and to reduce to a minimum the losses of glyoxylic acid during the subsequent concentration operations, it has been proposed to manufacture firstly, during the oxidation process, solutions of glyoxylic acid which are already relatively concentrated, that is to say having a content of glyoxylic acid of from 20 to 40% by weight, so as to reduce to a minimum the adverse effects of the subsequent concentration operations, the latter being generally carried out, in these known methods, on technical solutions of glyoxylic acid at about 50%.

In these known methods there is employed an aqueous solution of glyoxal with a concentration of from 30 to 50%, which is treated at a temperature of about 40 C. with an aqueous solution of nitric acid having a concentration of from 30 to 65%, the proportion of nitric acid being of the order of one molecule per molecule of glyoxal. The solution of glyoxylic acid obtained, having a concentration of from 20 to 40%, is converted to a technical solution at about 50% by applying generally the following steps: addition of alcohol in order to temporarily arrest to a certain extent the secondary oxidation by nitric acid, and in order to decompose this product, at least partially, to nitrogenized derivatives (still oxidizing); a first concentration under vacuum; cooling in order to cause crystallization of a part of the oxalic acid formed, which is eliminated; a new oxidation operation for hours at 40 C., in order to eliminate a further portion of the nitric acid and the oxidizing nitrogenized derivatives remaining; a second concentration under vacuum in order to bring the solution to the desired concentration of 50% of glyoxylic acid.

In spite of all the precautions mentioned, the methods in question do not result in the preparation of completely stable solutions since, apart from the other impurities, there always remain oxidizing nitrogenized products in the final technical solution of glyoxylic acid at 50%. In addition, the concentration operations cause a substantial conversion of glyoxylic acid to oxalic acid, so that the yield in glyoxylic acid found after the oxidation is considerably reduced after the preparation is completed.

The method of the present invention permits these serious drawbacks to be entirely avoided, at the same time offering the possibility of using very dilute solutions of glyoxal, for example crude solutions such as those resulting from the oxidation, in dilute solution, of acetaldehyde by nitric acid. It also enables the yield to be substantially increased, since the glyoxal which has not reacted during the oxidation can be recovered and re-cycled.

The invention consists in the manufacture of a stable and pure glyoxylic acid, in an aqueous solution or as a crystallized monohydrate, HOCCO H.H O, by producing in a first stage by the oxidation of an aqueous solution of glyoxal with nitric acid a crude solution of gyloxylic acid having a concentration comprised between 5 and 30%, preferably from 10 to 20%, in then eliminating the nitric acid from the crude solution of glyoxylic acid by the action of compounds acting as ion exchangers so as to obtain a stable solution, as yet impure, of glyoxylic acid, and in subjecting this stable solution to operations of purification and concentration, in particular by passage over ion exchangers and by crystallization.

The applicant has in fact found that by carrying out the oxidation under conditions such that there is a formation of a solution of glyoxylic acid with a concentration comprised between 5 and 30%, and preferably between 10 and 20%, the subsequent operations characteristic of the inventionin particular the passage over ion exchangers for the complete elimination of the nitric acid-are made possible with maximum effectiveness. In addition, under these conditions, oxalic acid is produced in a minor amount.

The elimination of nitric acid from the crude solution of glyoxylic acid by the action of compounds working as ion exchangers under the conditions prescribed by the invention must be sufficiently complete so as to give a solution of glyoxylic acid which is completely stable during storage and which can be subjected, without any substantial loss of glyoxylic acid, to the subsequent additional operations of purification and concentration.

According to a particular feature of the invention, the stable solution of glyoxylic acid, freed from nitric acid, is subjected to a further passage over an ion exchanger, under appropriate conditions, in order to eliminate the oxalic acid.

A further particular feature of the invention consists in subjecting the solutions of glyoxylic acid, freed from nitric and oxalic acids, to successive concentrations and crystallizations so as to collect the glyoxylic acid in the form of crystals having the formula HOCCO H.H O, with a degree of purity of at least 99% In order to carry into effect the method according to the invention, in the oxidation stage which is directed to the production of a crude solution of glyoxylic acid having a concentration comprised between 5 and 30%, the preferred conditions to be applied are as follows: There are employed solutions of glyoxal at a concentration preferably comprised between 7 and 30%, for example a commercial solution of glyoxal with a concentration in the vicinity of 30%, or a crude solution of glyoxal with a concentration in the neighbourhood of 10%, such as is produced for example by the oxidation of a dilute solution of acetaldehyde with nitric acid.

The nitric acid is utilized at a concentration preferably greater than 25%, in a proportion preferably comprised between 1 and 2 molecules per molecule of glyoxal utilized; more particularly, the preferred proportion of nitric acid approaches one molecule for more concentrated solutions of glyoxal, and is closer to two molecules for more dilute solutions of glyoxal.

The oxidation temperature is preferably comprised between 40 and 90C., more particularly, the preferred temperature approaches closer to 40 C. for the more concentrated solutions of glyoxal and closer to 90 C. for the more dilute solutions of glyoxal.

The elimination of nitric acid from the crude solution of glyoxylic acid is effected by means of a resin ion exchanger of the selective anionic type; there are preferably employed resins of the weak base or medium base type, such as those containing, for example, secondary or tertiary amine groups.

The preferred method of operation consists in utilizing a resin of this kind which, after regeneration by an alkaline solution, has been saturated with glyoxylic acid free from nitric acid. The percolation of the crude solution is then effected in such manner as to replace the glyoxylic acid fixed on the resin by the nitric acid of the crude solution of glyoxylic acid. By operating in this way, at the end of the operation there is obtained an effluent which contains practically the whole of the glyoxylic acid employed, while the nitric acid is practically wholly fixed on the resin.

The solution of glyoxylic acid obtained, free from nitric acid, can be subjected to a further passage over an ion exchanger of the type defined above in order to separate out the oxalic acid. The resin is utilized in its actual state, after regeneration by an alkaline solution. After this treatment, the solution is practically free from oxalic acid (and nitric acid), but it still contains impurities, in particular unconverted glyoxal.

This solution can then be subjected, according to the invention, to successive concentrations and crystallizations, in order to produce crystals of practically pure monohydrate glyoxylic acid. The preferred method of operation consists in concentrating the said solution to about 65% by weight of glyoxylic acid, preferably un der vacuum at a temperature not exceeding 40 C., in then cooling to the ambient temperature or below, if necessary after addition of germ crystals, so as to cause crystallization of the monohydrate glyoxylic acid; the crystals are separated from the mother liquors, for example by natural drying; they are rinsed with a very small quantity of water and then dried.

The mother liquors mixed with the rinsing water are again concentrated to about 65% and then crystallized, and this cycle of operations is carried out for as many times as may be necessary to collect preferably a maximum quantity of crystals, for example 85 to 90% of the glyoxylic acid in the form of monohydrate crystals.

The final mother liquors which contain the unconverted glyoxal and the uncrystallized glyoxylic acid are sent back into the manufacturing circuit.

The crystallized glyoxylic acid thus obtained has generally a content of 99 to 99.4% of monohydrate, the remainder being water.

In order that the invention may be better understood, two examples of its application are given below, by way of indication only and without any limitative sense.

Example 1 There are reacted at 40 C., with agitation, 406 kgs. of a commercial solution of glyoxal at 28. 3% by weight .and 395 kgs. of nitric acid at 31.6%. The reaction is continued until the solution has a concentration in glyoxylic acid of 16.3% by Weight. After the oxidation is stopped, there is obtained a solution comprising 123.6 kgs. of glyoxylic acid together with impurities: glyoxal, nitric acid and a little oxalic acid.

The solution obtained is passed over an ion exchanger resin such as is known commercially by the name of Lewatit MIH 59 (of the Bayer Company) for instance, previously saturated with glyoxylic acid, which gives a solution of glyoxylic acid practically free from nitric acid.

This solution is again passed over a selective ion-exchanger resin having an anionic nature, previously regenerated by an alkali, which yields a solution of glyoxylic acid containing practically no oxalic acid.

The solution is then concentrated under vacuum at about 40 C., up to a concentration of glyoxylic acid of about 65% by weight. This is then cooled in order to cause crystallization of the monohydrate glyoxylic acid, which is separated out.

The mother liquors are again concentrated to about 65% and then crystallized; this cycle of operations is then repeated a third time.

There is thus obtained a monohydrate glyoxylic acid of 99.4%, thus extremely pure.

Taking account of the small proportion of glyoxylic acid which remains in the mother liquors (and which is sent back into the manufacturing circuit), there are collected at the end of the operation 118.3 kgs. of glyoxylic acid, expressed as 100% anhydrous, which represents a yield of 95.7% with respect to the glyoxylic acid which was present at the end of the oxidation operation.

Example 2 There are reacted at C., with agitation, 221 kgs. of a crude technical solution of glyoxal at 11.4% and 65.8 kgs. of nitric acid at 63.2%, until the solution has a concentration in glyoxylic acid of 9.7% by weight. After the oxidation is stopped, there is obtained a solution comprising 27 kgs. of glyoxylic acid together with impurities: glyoxal, nitric acid and very little oxalic acid.

The solution obtained is passed over an ion-exchanger resin as in Example 1, in order to separate out firstly the nitric acid and then the oxalic acid.

The solution is then concentrated and crystallized as in Example 1.

There is thus obtained a monohydrate glyoxylic acid of 99.4%, thus extremely pure.

Taking account of the small proportion of glyoxylic acid which remains in the mother liquors (and which is sent back into the manufacturing circuit), there are collected at the end of the operation 26.2 kgs. of glyoxylic acid, expressed as anhydrous, which represents a yield of 97% with respect to the glyoxylic acid which was present at the end of the oxidation operation.

I claim:

1. In a method of manufacturing stable glyoxylic acid comprising oxidizing glyoxal in an aqueous solution with nitric acid and recovering glyoxylic acid from the resultant mixture, the improvement of obtaining stable glyoxylic acid having a purity close to 100% comprising effecting said oxidation of glyoxal at a concentration of 730% in said aqueous solution with said nitric acid at a concentration greater than 25% in a proportion of 1-2 moles of nitric acid per mole of glyoxal and at a temperature of 4090 C. to obtain a crude solution of glyoxylic acid at a concentration between 5 and 30% and containing nitric acid and a minor amount of oxalic acid;

removing the nitric acid from said crude solution by contacting said solution with an anionic ion exchange resin initially saturated with glyoxylic acid and free from nitric acid, said anionic ion exchange resin being selected from the group consisting of weak base and medium base types of anionic resins containing amine groups selected from the group consisting of secondary and tertiary amine groups;

removing the oxalic acid from said solution free of nitric acid by contacting said solution with an anionic ion exchange resin previously regenerated by an alkaline solution, said anionic ion exchange resin being selected from the group consisting of weak base and medium base types containing amine groups selected from the group consisting of secondary and tertiary amine groups;

and recovering the glyoxylic acid from said solution.

2. A method in accordance with claim 1, wherein said crude solution contains between 10 and 20% of glyoxylic acid.

3. A method in accordance with claim 1, wherein said recovering comprises crystallizing said glyoxylic acid from said solution.

4. A method of manufacturing crystalline glyoxylic acid in accordance with claim 1, wherein said recovering is eifected by concentrating said solution after contacting with said ion exchange resin up to about 65% by weight of glyoxylic acid, said concentration being carried out under vacuum at a temperature up to about 40 C.,

and then cooling said solution to about room temperature; further comprising separating the resultant crystals from the mother liquor by drying; rinsing with water; and then drying.

References Cited by the Examiner UNITED STATES PATENTS 2,469,684 5/1949 Dudley 260-538 10 2,664,441 12/1953 Owens et a1. 260-53 8 FOREIGN PATENTS 933,987 10/1955 Germany. 1,002,309 2/1957 Germany.

15 LORRAINE A. WEINBERGER, Primary Examiner.

LEON ZITVER, Examiner.

I. R. PELDMAN, R. K. JACKSON, Assistant Examiners. 

1. IN A METHOD OF MANUFACTURING STABLE GLYOXYLIC ACID COMPRISING OXIDIZNG GLYOXAL IN AN AQUEOUS SOLUTION WITH NITRIC ACID AND RECOVERING GLYOXYLIC ACID FROM THE RESULTANT MIXTURE, THE IMPROVEMENT OF OBTAINING STABLE GLYOXYLIC ACID HAVING A PURITY CLOSE TO 100% COMPRISING EFFECTING SAID OXIDATION OF GLYOXAL AT A CONCENTRATION OF 7-30% IN SAID AQUEOUS SOLUTION WITH SAID NITRIC ACID AT CONCENTRATION GREATER THAN 25% IN A PROPORTION OF 1-2 MOLES OF NITRIC ACID PER MOLE OF GLYOXAL AND AT A TEMPERATURE OF 40-90*C. TO OBTAIN A CRUDE OIL SOLUTION OF GLYOXYLIC ACID AT A CONCENTRATION BETWEEN 5 AND 30% AND CONTAINING NITRIC ACID AND A MINOR AMOUNT OF OXIALIC ACID; REMOVING THE NITRIC ACID FROM SAID CRUDE SOLUTION BY CONTACTING SAID SOLUTION WITH AN ANIONIC ION EXCHANGE RESIN INITIALLY SATURATED WITH GLYOXYLIC ACID AND FREE FROM NITRIC ACID, SAID ANIONIC ION EXCHANGE RESIN BEING SELECTED FROM THE GROUP CONSISTING OF WEAK BASE AND MEDIUM BASE TYPES OF ANIONIC RESINS CONTAINING AMINE GROUPS SELECTED FROM THE GROUP CONSISTING OF SECONDARY AND TERTIARY AMINE GROUPS; REMOVING THE OXIALIC ACID FROM SAID SOLUTION FREE OF NITRIC ACID BY CONTACTING SAID SOLUTIION WITH AN ANIONIC ION EXCHANGE RESIN PREVIOUSLY REGENERATED BY AN ALKALINE SOLUTION, SAID ANIONIC ION EXCHANGE RESIN BEING SELECTED FROM THE GROUP CONSISTING OF WEAK BASE AND MEDIUM BASE TYPES CONTAINING AMINE GROUPS SELECTED FROM THE GROUP CONSISTING OF SECONDARY AND TERTIARY AMINE GROUPS; AND RECOVERING THE GLYOXYLIC ACID FROM SAID SOLUTION. 